A color filter substrate is used in a liquid crystal display device and the like. The color filter substrate generally includes, on a glass substrate, a black matrix (BM) for shielding a space between color patterns, and colored layers of red (R), green (G), and blue (B) formed in a pixel. Examples of a production method of the color filter substrate include a pigment dispersion method, a staining method, an electrode position method, a printing method, and an ink-jet method. Particularly, according to the ink-jet method, color materials of red (R), green (G), and blue (B) are injected into a region partitioned by the bank while an ink-jet head is moved, and thereby a colored layer pattern is directly formed. This method needs no exposure and development steps, and therefore, a use amount of the material for the colored layers is reduced, and simplified production processes reduces production costs.
Such a color filter substrate is generally arranged as a substrate different from an active matrix substrate for controlling driving of pixels. A Color-filter On Array (COA) structure in which a color filter is formed on the active matrix substrate is now being proposed. According to such a COA structure, there is no need to position pixels on the active matrix substrate with those on the color filter substrate, and a width of a bank pattern can be further decreased. Therefore, an aperture ratio can be improved. An attempt to produce a color filter with a high aperture ratio by combination use of the ink-jet method and the COA technology at low costs has been made (for example, refer to Patent Document 1).
However, as shown in FIG. 13, if a structure in which an insulating film 44 is formed on a substrate 1, and on the insulating film 44, a bank 3 and a colored layer 42 in a region surrounded by the bank 3 are formed is formed by a conventional ink-jet method, the colored layer 42 has a domed surface whose top is positioned in the center. As a result, the entire color filter substrate has an irregular surface. Therefore, a reverse tilt region (domain) in which an alignment direction of liquid crystal molecules in a liquid crystal layer is opposite to its normal direction is generated near the boundary between the colored layer 42 and the bank 3, and at this region, light leakage is caused, which affects display qualities. In this point, there is room for improvement.
Under such a circumstance, a method in which a flattening layer (transparent protective layer) is arranged on the colored layer or the BM to improve the flatness (for example, refer to Patent Documents 1 and 2) has been disclosed. However, if such a method is applied to a CF substrate having the above-mentioned COA structure, a step of additionally forming a contact hole in the flattening layer to connect a pixel electrode to an electrode of a thin film transistor is needed. Such a method still has room for improvement because merits of the ink-jet method, such as simplification of processes and reduction in costs, are not advantageously used.
[Patent Document 1]
    Japanese Kokai Publication No. 2002-131735[Patent Document 2]    Japanese Kokai Publication No. 2002-341128